Protecting Naperville’s Ash Trees

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When the emerald ash borer was discovered in Naperville in 2008, the city had almost 18,000 ash trees – all put at risk by the destructive insect.

Today, over 13,000 are still standing. A much better outcome than the complete devastation other communities have seen.

“It can go from just a few beetles in your community to, within a few years, millions of beetles that are affecting all of your ash trees,” said Jack Mitz, City Forester of Naperville.

The beetles destroy the tree’s ability to take up nutrients and water. So helping the trees defend themselves is the first part of Naperville’s program to fight them.

Insecticides are injected into the trunk, or into the soil for the roots. The tree then absorbs the chemical, and as beetle larvae eat the wood, they’re killed off, keeping damage low enough that the tree can heal and survive.

The other part of the program is removing dying trees to slow down the spread of the infestation.

“If the trees are left standing and they haven’t been treated, then once the beetles kill that tree they move on, they fly off and go to other trees and infest those trees,” said Mitz.

But treating and saving the trees is a lot cheaper than removing and replacing them. While the average removal and replacement costs $625, the average annual cost of treatment for a tree is just $35.

This makes the $800,000 a year program a long-term cash saver for taxpayers.

And the city is trying to minimize future costs by taking steps to prevent an infestation like this from happening again.

“The biggest thing is we replace ash trees with a mixture of species,” said Mitz. “We’re trying to diversify the urban forest. That’s the biggest thing anyone has learned out of this whole episode.”

By planting a wider variety of trees, no single invasive species can threaten the entire city’s tree population.

Naperville News 17’s Blane Erwin reports.